Depends on what harness you are refering to. If you mean the engine harness then you can use the 77 if you mean the front body harness you might want to find a 75/76. Now Megasquirt is only an engine harness.
Painless sells a nice wiring kit but is pricy. There is a cheaper alternative
http://www.autowiringsolutions.com/item.php?item_id=261